1. Field of the Invention
The present invention relates to an image reading apparatus in which, while a film having a plurality of frame images formed thereon is conveyed, a plurality of the frame images are read by reading light emitted from a light source and transmitted through or reflected from the frame images, by using a line scanner.
2. Description of the Related Art
In recent years, a technique is known in which frame images recorded on a photographic film are optically read by a reading sensor such as a CCD (charge coupled device) or the like, image processing such as enlargement and/or contraction, various corrections, or the like is performed with respect to digital image data obtained from the aforementioned reading, and an image is thereby formed on a recording material by using laser light which is modulated on the basis of digital image data for which the image processing has been completed.
In such a technique in which frame images are digitally read by the reading sensor such as the CCD or the like as described above, in order to realize highly accurate image reading, frame images are read preparatorily (so-called prescanning), reading conditions in accordance with densities or the like of frame images (for example, amount of light to be irradiated onto the frame images, time during which charge is accumulated in the CCD or the like) are determined, and the frame images are again read on the basis of the determined reading conditions (so-called fine scanning).
In this case, since prescanning can be performed with relatively low image-reading accuracy, prescanning has a relatively high tolerance for irregularity in the speed at which a recording material is conveyed. On the other hand, since fine scanning must be performed at as high speed as is possible and with extremely high image-reading accuracy, fine scanning has an extremely limited tolerance for variation in the amount of light or noise generated when frame images are read.
However, because a conventional halogen lamp that has been in general use for printing exposure or the like generates an excessive amount of heat, light emission efficiency deteriorates, and increasing the speed for reading images is thereby restricted.
Although the halogen lamp is the most suitable light source for a printing exposure in which the light source is transmitted through a negative film so as to print an image directly on a printing paper, as described above, in a system in which the image is read by the CCD, since the halogen lamp has a low color temperature, and emits a low amount of light having a short wavelength (bluish colors when speaking in terms of color), and the SN ratio of the image read thereby deteriorates (includes an excessive amount of red when speaking in terms of color). Also, the halogen lamp hinders images from being read at high speed.
In order to solve this, a discharge lamp having a high color temperature (e.g., a xenon lamp or a metal halide lamp) can be thought of, as a light source. However, there is a drawback in that discharge noise is generated so that images cannot be read with high accuracy.
It is an object of the present invention to provide an image reading apparatus in which the illumination light amount for each color is well-balanced by using a light source that generates a small amount of heat during light emission thereof and has a high color temperature, such that an image can be read at high speed and with high accuracy.
A first aspect of the present invention is an image reading apparatus that, while a film having a plurality of frame images recorded thereon is conveyed, reads a plurality of said frame images by reading light emitted by a light source and transmitted through or reflected from said frame images, using a line scanner, wherein said light source comprises: a plurality of light emitting elements that emit lights of colors corresponding to light having substantially the same wavelengths; and a photoconductive member that includes a light entering surface which faces said plurality of the light emitting elements and into which light emitted by said plurality of light emitting elements enters, and a light exiting surface which faces said film and from which light that enters the light entering surface exits.
In accordance with the first aspect of the present invention, the light emitting elements generally emit a small amount of light, but the color temperature is high and a large amount of the light has short wavelengths. Thus, light having such characteristics as described above enters the light entering surface and exits from the light exiting surface losing almost no light. Because a film is placed so as to face this light exiting surface, almost the entire amount of light that exits the light exiting surface can be irradiated onto the film.
As described above, generally, the light emitting elements emit a small amount of light. In accordance with the first aspect of the present invention, a plurality of these light emitting elements are applied to assure a necessary amount of light. In the present invention, because a light source is selected giving weight to how high the color temperature is, rather than selecting a light source that outputs a large amount of light at a time, an insufficient amount of light is compensated for by the number of light sources. Accordingly, for example, even when a CCD line sensor or the like is used as a line scanner, the SN ratio of an image when the image is read can be improved.
A second aspect of the present invention is an image reading apparatus according to the first aspect of the present invention, wherein said wavelengths are that of lights of three colors consisting of B (blue), G (green), and R (red).
In accordance with the second aspect of the present invention, when a color image is read, light emitting elements of the three colors, i.e., B (blue), G (green), and R (red) must be used. The light emitting elements having wavelengths corresponding to each of the three colors are disposed. Accordingly, in a case in which the light emitting elements of the three colors are mixed with one another, white light can be created.
A third aspect of the present invention is an image forming apparatus according to the first aspect of the present invention, wherein said plurality of said light emitting elements are arranged so as to form straight lines, at a high density.
In accordance with the third aspect of the present invention, the plurality of the light emitting elements are arranged so as to form substantially straight lines, at a high density, along the direction in which the line scanner scans, for example. Accordingly, reading cells (pixels) of the line scanner are divided in accordance with the number of the light emitting elements are parted into pluralities of pixels. Thus, a necessary (corresponding) amount of light can be provided. In this case, since the light emitting elements have a high color temperature and can be irradiated stably with high illuminance, color unevenness is not caused among the light emitting elements.
A fourth aspect of the present invention is an image reading apparatus according to claim 1, wherein the plurality of the light emitting elements are LEDs.
In accordance with the fourth aspect of the present invention, the LED is a most suitable light emitting element. The LED can easily control light, can be manufactured inexpensively, and has a long life. Namely, the LED is most suitable, as a light emitting element that can satisfy both direct requirements such as color temperature and the like, and indirect requirements such life length as described above.
A fifth aspect of the present invention is an image reading apparatus according to the first aspect of the present invention, wherein a reflecting member having a predetermined reflectance is adhered to surfaces of the photoconductive member other than the light entering surface and the light exiting surface such that the reflecting surface of the reflecting member faces inward.
In accordance with the fifth aspect of the present invention, light incident on the photoconductive member is reflected off the surfaces other than the light exiting surface by the reflecting member. Accordingly, there is no difference between the amount of light that enters the light entering surface and the amount of light that exits from the light exiting surface. As a result, it is possible to increase an effective amount of light.
A sixth aspect of the present invention is an image reading apparatus according to the second to the fifth aspects of the present invention, wherein the lights of the three colors are mixed evenly with one another and irradiated onto the film.
In accordance with the sixth aspect of the present invention, the light emitting elements of three colors are mixed evenly with one another so that white light can be formed and irradiated onto a film. Accordingly, an image of the same region of the film is formed on each of the reading portions of the line sensor corresponding to each of the colors of the light emitting elements. As a result, the same image can be read at once.
A seventh aspect of the present invention is an image recording apparatus according to the second to fifth aspects of the present invention, wherein the lights of the three colors are respectively irradiated onto different regions of the film in a state in which the three colors are separated from one another.
In accordance with the seventh aspect of the present invention, lights emitted by the light emitting elements of the three colors are introduced independently from one another, and are irradiated onto the different regions of the film. Since the line sensor receives transmitted light or reflected light from each of the regions of the film, color separation ability can be improved.